Conformational and vibrational analysis of gamma-aminopropyltriethoxysilane

A comprehensive conformational and vibrational analysis has been carried out on gamma-aminopropyltriethoxysilane (APTES) by density functional theory (DFT) using Becke’s three-parameter exchange functional in combination with the Lee–Young–Parr correlation functional (B3LYP) and standard 6-31G(d, p) basis set. The scanning of the potential energy surface with respect to the SiCCC torsion angle suggests that there are five stable conformations. There are two minima with trans (t1, t2) conformations as well as three local minima corresponding to gauche (g1, g2, g3) conformations. The lowest energy conformer has trans-t1 structure with SiCCC dihedral angle of 178.8°. The gauche conformers with torsion angle around 70° have various orientations of ethoxy chains. The calculated barriers to the conformation interchange are: 114, 484, 1272, 1239 and 1120 cm−1 for the trans-t1 to trans-t2, trans-t1 to gauche-g1, trans-t1 to gauche-g2, trans-t2 to gauche-g2 and gauche-g2 to gauche-g3 conformers, respectively. The infrared (500–4000 cm−1) spectra and Raman (50–3500 cm−1) spectra of liquid APTES with qualitative polarization measurements have been recorded. A complete vibrational assignment for APTES conformers is supported by the normal coordinate analysis, calculated IR intensities as well as Raman activities. On the basis of the results, the vibrational spectra of APTES have been analyzed. The average error between the observed and calculated frequencies is 10 cm−1.